This invention relates to powertrains having multi-speed transmissions and particularly to six speed planetary transmissions that include three planetary gear sets.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration. It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. One such transmission is disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978. The Polak transmission provides six forward speed ratios. Six speed transmissions offer several advantages over four speed transmissions, including improved vehicle acceleration and improved fuel economy. However, passenger cars still employ three and four speed automatic transmissions with a few five speed devices due to the size and complexity of six speed transmissions.
It is an object of the present invention to provide an improved six speed planetary transmission.
In one aspect of the present invention, the transmission has minimum mechanical content including three planetary gear sets. In another aspect of the present invention, the transmission has five torque transmitting mechanisms in the form of selectively engageable, fluid-operated clutches and brakes. In yet another aspect of the present invention, the transmission employs two clutches and three brakes.
In still another aspect of the present invention, the transmissions output shaft is continuously connected for common rotation with one member of one of the planetary gear sets and the input shaft is continuously connected for common rotation with at least one member of another of the planetary gear sets. In a further aspect of the present invention, two gear members of the first planetary gear set are continuously interconnected with two gear members of the second planetary gear set. In a yet further aspect of the present invention, a third gear member of the second planetary gear set and one gear member of the third planetary gear set are continuously interconnected for common rotation.
The present invention is comprised of a family of transmissions having three planetary gear sets. The planetary gear sets may be either of the simple type or the compound type. Each planetary gear set has three gear members, namely, a sun gear member, a ring gear member, and a planet carrier gear member. A first member and a second member, respectively, of each of the first and second of the planetary gear sets are interconnected for continuous common rotation, and a third member of the second of the planetary gear sets and a member of the third of the planetary gear sets are interconnected for common rotation. At least one member of one of the planetary gear sets is continuously connected with an input shaft for common rotation therewith, and at least one member of one of the planetary gear sets is continuously connected with an output shaft for common rotation therewith.
The transmission includes five selectively engageable, fluid-operated torque transmitting mechanisms, two of which are rotating torque transmitting mechanisms (clutches) and three of which are stationary torque transmitting mechanisms (brakes). The torque transmitting mechanisms are interconnected with the planetary gear sets to establish six forward ratios and one reverse ratio. One of the rotating torque transmitting mechanisms is operable to provide an input drive connection, and the other rotating torque transmitting mechanism is operable to provide either a gear member to gear member interconnection or an output drive connection.